U.S. Coach Juergen Klinsmann made a valid point on May 29 when he said this after a 4-2 friendly loss to Belgium:

“There’s a lot we can learn from these opponents. This is why we play teams like Belgium, like Germany, like Russia or like Italy because there’s so much that you can read from those games. Obviously you want to win them and when you lose them it’s not such a big pleasure, but I’d rather play Belgium 10 more times than El Salvador 100 times because that’s where you learn.”

Playing a world-class opponent is, of course, more beneficial to Klinsmann’s charges than facing a CONCACAF side (other than Mexico). Where the United States is situated in the world order, behind the Euro and Latin titans but well ahead of almost all regional rivals, the Americans need matches outside their cozy neighborhood to push themselves, to measure their progress, to make gains ahead of the 2014 World Cup in Brazil.

When Klinsmann referenced El Salvador, he wasn’t singling out El Salvador. He could have just as easily mentioned Guatemala or Canada. But he did mention El Salvador. And now, just seven weeks later, he is preparing for a consequential match against El Salvador in the Gold Cup.

Salvadoran supporters and media are rallying around Klinsmann’s throwaway line in Cleveland. One Salvadoran reporter told me the quote has further galvanized the burgeoning Salvadoran community in the United States. Heavy underdogs find inspiration in all places before a major challenge, and a perceived slight by an opposing coach feeds their fire. Whatever works.

The Salvadoran squad, which squeaked into the quarterfinals as a third-place team in group play, will ride an emotional wave Sunday afternoon against the United States in Baltimore. With tens of thousands of recent Salvadoran immigrants and Salvadoran-Americans from the Washington-New York corridor gobbling up tickets the past five days, a sea of blue promises to wash over purple-splashed M&T Bank Stadium. The addition of Honduran blue, as well as American red and blue and Costa Rican red for the doubleheader, will create a tapestry celebrating American diversity and a sport that embodies our multiculturalism.

Some will argue everyone in America should root for America. It’s not that simple. Your family roots (just like your alma mater and favorite childhood team) are in your soul. You can move a Redskins fan out of Washington but you can’t extract burgundy-and-gold from one’s being. Would an Alabama alum living in Oklahoma ever root for the Sooners? Heck, no.

Organizers in Baltimore are bracing for a sellout crowd of approximately 69,000. As of Thursday evening, 85 percent of tickets were gone. The fact that U.S. supporters will be in the minority in their own country will trouble some and feed dwindling anti-soccer forces that cling to outdated beliefs that soccer will remain a “foreign” sport here. No, actually, soccer here is a diverse sport cutting through ethnic, racial, religious, cultural and class boundaries. (Compare a soccer audience to, say, a largely homogeneous golf or baseball crowd.)

Soccer has followed America’s demographic shift, influenced the past 25 years by Latin American arrivals. Salvadorans are a big part of the transformation. To feed their hunger for soccer, local promoters wisely stage a Salvadoran national team match at RFK Stadium at least once a year. Crowds have ranged from 10,000 to 40,000, depending on the opponent, time of year and whether La Selecta is in good form.

Salvadorans were a block in D.C. United’s foundation upon MLS’s launch in 1996, turning out to see countryman Raul Diaz Arce score bundles of goals. When the club traded him, Salvadoran fans felt betrayed. United never fully won them back, even after signing other (lesser) Salvadoran players.

In San Salvador, the national team plays at Estadio Cuscatlan. On those days when the ES squad visits, RFK may as well be called Cuscatlan Norte. (If United ever builds a stadium at Buzzard Point, the Salvadoran soccer federation should make an offer for RFK.)

Last month El Salvador’s under-20 squad drew about 10,000 at Maryland’s Byrd Stadium for a friendly against a young Honduran team. Four ES players were raised and schooled in this area, sons of Salvadoran immigrants.

Will the large Salvadoran presence in Baltimore on Sunday influence the outcome? Maybe. The U.S. squad, though, is accustomed to home “away” games against Mexico and Honduras, among others, in diverse markets, such as Los Angeles and Washington. Nonetheless, in an effort to boost last-minute support, the U.S. Soccer Federation reached out to fans on its e-mail list Thursday night, offering $5 discounts for tickets purchased with a special online code. The USSF said the concept came from CONCACAF.

Even with a secondary roster for the Gold Cup, the Americans have a pronounced advantage in personnel. They have won eight straight games — three World Cup qualifiers, three Gold Cup matches and two friendlies — to set a program record. Landon Donovan, America’s scoring king, is rounding back into form after a national team hiatus. Reinforcements began arriving Thursday as teams were allowed to make roster changes before the knockout rounds. Klinsmann has the player pool depth to weigh such decisions; most small countries do not.

Despite a 1-15-5 record against the United States — the only victory came 21 years ago — El Salvador is no pushover: In the past three meetings, there were a pair of 2-1 outcomes on U.S. soil and a 2-2 draw in San Salvador. Only one of the previous eight encounters were decided by more than two goals. Forward Rodolfo Zelaya is a rising star in the CONCACAF region, forging an electric partnership with playmaker Osael Romero.

Midfielder Richard Menjivar, just 22, was born in Los Angeles, attended the University of Evansville and Cal State Bakersfield, represented the United States at the under-18 level, broke through with former U.S. star Eric Wynalda‘s Cal FC amateur side, and now plays for the Atlanta Silverbacks, a second-division pro team.

He, like many in the Baltimore crowd, has ties to two nations. For this, regardless of Sunday’s result, soccer in America is the true winner.

Steven Goff is The Post’s soccer writer. His beats include D.C. United, MLS and the international game, as well as local college basketball.

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